Before using this function you'll need to call FacebookLogin() and ensure the user is logged in with GetFacebookLoggedIn() at which time you'll be able to call FacebookGetFriends() until FacebookGetFriendsState() returns 1.
Please refer to the help on those function for proper usage.

The proper usage for FacebookPostOnFriendsWall() is as follows:
fbindex = round(FBfriendsListUI#[nameIndex , 4])
fbid$ = FacebookGetFriendsID ( iIndex ) //who's wall you want to post to
fbName$ = FacebookGetFriendsName ( iIndex ) //their name for reference if you like
firstName$ = GetStringToken(fbName$ , " " , 1) //just getting their first name here
name$ = "Wordspionage" //this is the name for the link
link$ = "http://www.wordspionage.com"
caption$ = "Go Beyond The Board" //a little caption
description$ = firstName$ + ", join me for a game of Wordspionage!"
pic$ = "http://wordspionagedb.com/fbposticon.png" //picture must be the web

FacebookPostOnFriendsWall(fbid$ , link$ , pic$ , name$ , caption$ , description$)


Facebook will fill in things if you don't use all the fields. For example, if you don't specify a picture then FB will grab the cover image for your website like it does with thumbnails for posts. It will also say something like "Check out http://www.wordspionage.com HOME PAGE" if you don't specify a description. 

Here's an image of what the about looks like on FB:
http://bit.ly/1cpbZO1